1. Field of the Invention
This invention relates to apparatus and methods for testing electrical connections between conductors on an insulating body by applying an electron beam to the surface of the device under test.
2. Related Art
U.S. Pat. Nos. 4,578,279; 4,417,203; and 4,415,851 (commonly assigned to the assignee of the instant application) all relate to use of E-beam testing of substrates.
U.S. Pat. No. 4,415,851 of Langner et al for "System for Contactless Testing of Multi-layer Ceramics" and U.S. Pat. No. 4,417,203 of Pfeiffer et al "System for Contactless Electrical Property Testing of Multi-layer Ceramics" disclose systems for testing of networks including both top to bottom and top to top connections. The systems include two E-beam flood guns and one scanning beam gun. The scanning beam is arranged to scan the top surface of the specimen under test. One flood gun irradiates the bottom surface for top to bottom testing. The other flood gun irradiates the top for testing top to top connections.
U.S. Pat. No. 4,578,279 of Zingher for "Inspection of Multilayer Ceramic Circuit Modules by Electrical Inspection of Unfired Green Sheets" describes employing electrical testing techniques including E-beam testing techniques.
W. H. Bruenger, F. J. Hohn, D. P. Kern, P. J. Coane, and T. H. P. Chang, "Electron Energy Analyzer for Applications in Large Scan Field for Electron Beam Testing", Proceedings of the Symposium on Electron and Ion Beam Science and Technology, Tenth International Conference 1982, The Electrochemical Society, Proceedings Vol. 83-2, pp. 159-169(1983) shows in FIG. 4 a four channel retarding field analyzer with successive extraction grid, "retard" grid and collector grid at a 45 degree angle to the vertical with respect to the target of the E-beam, with a sensor and photomultiplier tube behind the collector grid.
P. J. Fentem and A. Gopinath "Voltage Contrast Linearization with a Hemispherical Retarding Analyzer", Journal of Physics E: Scientific Instruments pp.930-933 (1974) Vol. 7, shows on page 931 a pair of hemispherical grids in both FIGS. 1a and 1b with grid B being a retarding grid. The article states, ". . . two hemispherical grids, which form the retarding analyzer, with the specimen at the centre." FIG. 1b shows a scintillator cage beyond the retarding grid B. With respect to the scintillator cage, the article states "Final collection was achieved . . . by placing a conventional scintillator cage detector close to the grids." It is stated in Fentem, et al with respect to FIG. 1a that grid A "is held at +60 V to ensure that secondary electrons emitted from the specimen are attracted outwards, although this results in the grid collecting some electrons. This grid should be at least, say, 15 V above the most positive potential applied to the retarding grid [B] because a rise in collected current at the solid hemisphere is observed when the potential of the retarding grid approaches that of the inner grid." From the point of view of this invention, Fentem, et al has drawbacks. Firstly, secondary electrons are caused to return to the sample. Secondly, there is no peak in the voltage contrast characteristic, the desirability of which is discussed later. Thirdly, the system is suitable only for relatively small samples.
S.D. Golladay, H.C. Pfeiffer, and M.A. Sturans, "Stabilizer Grid for Contrast Enhancement in Contactless Testing of MLC Modules", IBM Technical Disclosure Bulletin Vol 25, No. 12, May 1983, pp. 6621-6623) shows testing with E-beams using a negatively biased stabilizer grid between a flood gun and a sample.
U.S. patent application Ser. No. 925,764, filed Oct. 30, 1986, now U.S. Pat. No. 4,843,330 of Golladay, Hohn and Pfeiffer for "Electron Beam Contactless Testing System with Grid Bias Switching" describes an electron beam testing system wherein a grid is located above the device under test. The grid is employed both to assist charging and to extract secondary electrons from the device under test by switching the bias voltage applied to the grid.